Ferrite microwave mixer



May 10, 1960 L. J. LADER 2,936,369

FERRITE MICROWAVE MIXER Filed Aug. 15, 1958 2 Sheets-Sheet 1 //WENTOR,

Y Lson J. LADER ATTORNEY y 0 L. J. LADER 2,936,369

FERRITE MICROWAVE MIXER Filed Aug. 15, 1958 2 Sheets-Sheet 2 SIGNAL OUTPUT 53 SIGNAL INPUT r PUMP INPUT 23 &

7 SIGNAL INPUT z fl rzmz Zia/v 4224054 Ivan 5% United States Patent FERRITE MICROWAVE MIXER Leon J. Lader, Los Angeles, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Application August 15, 1958, Serial No. 756,061

12 Claims. (Cl. 250-20) The present invention relates to a microwave frequency mixer and more particularly to a ferrite microwave mixer of two signals having different frequencies for obtaining a signal with a substantially low difference frequency.

Frequency mixing is generally accomplished by crystals or vacuum diodes. The diodes have never proven satisfactory at microwave frequencies and so crystals have been depended upon for such function. Where replacement of crystals is not practical as in airborne equipment, it has been found that a more reliable device is required because crystals are frequently subject to deterioration or burnout when a small excess of power occurs. Further, elaborate systems and additional devices are frequently required to protect the crystals during operation of the equipment.

With the knowledge that has been obtained in recent years with respect to the characteristics of gyromagnetic materials at the frequency of microwave energy, many new components have been developed to simplify microwave systems and at the same time increase operational reliability thereof. There has now been developed a ferrite microwave frequency mixer that, in general, comprises a coaxial section of transmission line having a suitably magnetized ferrite cylinder coaxially mounted therein with a pickup coil wound about the center conductor or the ferrite cylinder. Microwave energy is electromagnetically coupled into the coaxial section at two different frequencies and is concentrated in the ferrite cylinder Where signals at the sum and difference frequencies are developed. A signal at the difference frequency is then induced in the pickup coil and suitably and selectively coupled out for use externally of the mixer device.

it is, therefore, an object to provide a new and improved frequency mixer for microwave energies;

Another object is to provide a system for mixing microwaves in the ferrite medium to produce a useable frequency translation of the input signals.

A further object is to provide concentration of microwave fields in a ferrite element to minimize power requirements for producing frequency translations.

A still further object is to provide a ferrite microwave filter for producing a difference frequency suitable for use as an intermediate frequency in microwave systems.

A still further object is to provide a ferrite loaded microwave device for frequency mixing or amplification depending upon the relative arrangement of the inputs and the values thereof.

Other objects and advantages of the invention will be apparent in the following description and claims considered together with the accompanying drawing, in which:

Figure l is a perspective view of a ferrite microwave mixer;

Figure 2 is a schematic view in section of the frequency translation section of Figure 1; and

Figure 3 is a schematic perspective view of a traveling wave embodiment of the invention of Figure 1.

Referring to Figure 1 in detail there is illustrated in ice perspective a pair of rectangular input waveguides 11 and 12, each respectively having an input port 13, 14 at one end and a conventional adjustable short 16 and 17 at the other end. The two waveguides 11 and 12 are mounted in parallel relation with suitable brackets (not shown) to maintain such relationship and 'with a translation secion 19 disposed intermediately and transversely between the waveguides.

As shown in Figure 2, the translation section 19 comprises a coaxial section of transmission line having a center conductor 21 and an outer conductor 22 with the ends of the latter respectively inserted into matching apertures 23 and 24 of waveguides 11 and 12. Conventional adjustable coupling probes 26 and 27 are respectively mounted at either end of the center conductor 21 to extend into the waveguides 11 and 12. Thus, as microwave energy is propagated through waveguides 11 and 12 in, for example, the dominant TE mode, the probes 26 and 27 electromagnetically couple to the electric fields of the modes and are excited thereby so that the amount ofenergy coupled is transmitted within translation section 19 in the dominantTEM mode. The adjustable shorts 16 and 17 are provided to minimize reflections and the voltage standing wave ratio of the waveguides 11 and 12.

For frequency translation in the coaxial section 19 a hollow cylinder 31 of gyromagnetic material, such as ferrite, is suitably mounted coaxially within the section and the magnetic fields of the two energies electromagnetically coupled into the section, extend circumferentially through the cylinder. Two magnetic pole pieces 33 and 34 are respectively mounted about the coaxial section 19 at the ends thereof and a conventional static magnetic field establishing device such as a permanent magnet 35 or an electromagnet is mounted in contact with the pole pieces. In accordance with the invention the static magnetic field, indicated by an arrow labled H extends parallel to the longitudinal axis of the cylinder 31 and is established at a value producing gyromagnetic resonance at the higher frequency of the two energies.

Under the foregoing conditions the magnetic field vectors associated with the microwave energies Within the ferrite cylinder 31 of the coaxial section 19 are perpendicular with respect to the static magnetic field vector so that precessional resonance occurs in the ferrite about the higher frequency and, because of the nonlinear characteristics of the ferrite, precessional instabilities occur about the sum and difference frequencies of the two energies. Now, it is well known that where magnetic field vectors of microwave energy are perpendicular to a static magnetic field vector in gyromagnetic material, energy is coupled from the microwave energy into modes orthogonal to the microwave magnetic field vectors. Thus, there are developed magnetic field components at the sum and difference frequencies of the two microwave energies and such components are along the direction of the static magnetic field.

To couple to the fields associated with the sum and difference frequencies within the coaxial section 19, a pickup coil 36 is, as illustrated, suitably wound on the center conductor 21 and two leads 37 and 38 thereof are respectively extended to terminals 41 and 42 through apertures 43 and 44 of cylinder 41 and through conventional insulators 46 and 47 suitably mounted through the outer conductor 22. It will be readily apparent that pickup coil 36 may be readily wound on the ferrite cylinder 31 Where closer inductive coupling is desired. A tuning capacitor 48 is connected between the two terminals 41 and 42 to provide a resonant circuit with the inductance of coil 36 for limiting signals induced in pickup coil 36 to a single frequency at such terminals.

In operation port 13 is coupled to a source of microwave energy (not shown), which will be referenced for convenience as a pump signal having a value of angular frequency denoted by the symbol u Similarly, port 14 is coupled to a source of microwave energy (not shown), which will be referenced merely as a signal and denoted by the angular frequency symbol u The two microwave energies are respectively propagated by waveguides 11 and 12 in the dominant TE mode. Probes 26 and 27 then electromagnetically couple to the respective electric fields of waveguides l1 and 12 to excite TEM modes in coaxial translation section 19.

The magnetic fields of the two TEM modes extend circumferentially and are concentrated in ferrite cylinder 31 transverse to the direction of the static magnetic field H Energy is then coupled or translated by the ferrite material into orthogonal modes along the direction of the static magnetic field to magnetically link pickup coil 36. An output signal is then induced in the coil 36 and connected to terminals 41 and 42. The foregoing operation is dependent upon the value of the static magnetic field being established to provide gyromagnetic resonance or precessional resonance at the frequency o of the pump signal.

In the foregoing the device of the present invention has been set forth as a frequency mixer and in this respect is defined by an output having an angular frequency w that has a substantially low value with respect to that of the pump signal m For example, where an output having a frequency of 30 me. per second is desired and the signal frequency is 4500 me. per second as applied to port 14, then the frequency of the pump signal is established at 4530 me. per second. The capacitor 48 is adjusted to resonate with the inductance of pickup coil 36 at 30 mc. per second to eliminate the sum frequency of 9030 me. per second.

In addition to providing a microwave frequency mix- 'ing operation, two other conditions of operation exist. One occurs when a high frequency pump signal is applied as before and a low frequency signal is applied as an input to terminals 41 and 42. In this instance, themagnetic field vector of the pump signal w is trans verse to the direction of the static magnetic field and the magnetic field of the low frequency signal a is along the direction of the static magnetic field. The result is a translation of energy by the ferrite material of cylinder 31 from that of the pump signal 01,, to a signal having a frequency ha which is the sum frequency of the two input signals.

The other condition occurs when a high frequency pump signal w is again applied in the same manner and the signal a of waveguide 12 has the same frequency as that of the output to The same magnetic field relationships exist and amplification of the signal w occurs by energy coupling from the pump signal w by the ferrite material. Because of the higher frequency of the signal under this condition of operation, the output must be electromagnetically coupled through a coaxial line.

By the concentration of the pumping power field in the ferrite material of cylinder 31 as provided by the structure set forth, the required power to produce the necessary non-linearities in the ferrite material for frequency translations and amplification is minimized. Also, it has been found in practice that the device is not subject to deterioration or burnout at substantial values of signal power and can actually withstand short duration pulses in the kilowatt range.

While the structure has been described as having two rectangular waveguides Ill and 12 coupled to the coaxial section 19 at opposite sides thereof, it will be apparent that coaxial lines could be readily used in place of the waveguides with suitable modification with respect to the probes 26 and 27. Also the two energies may be coupled by a single waveguide at one end of the coaxial section with a suitable termination provided at the other end.

Substantially the same operation, based upon the same principles as set forth in the foregoing for the device of Figures 1 and 2, can be obtained from a traveling wave structure as illustrated in Figure 3. Thus, in the perspective view of the latter figure, there is shown a section of rectangular waveguide 51 having respective input ports 52 and 53 at either end. Such waveguide 51 is dimensioned to propagate microwave energies of two different frequencies in the same type of mode, which have magnetic fields polarized along planes parallel to the broad walls of the waveguide.

Frequency translation is accomplished Within the waveguide by a cylindrical post 56 of gyromagnetic material, such as ferrite, suitably mounted transversely between the broad walls. A static magnetic field, indicated by an arrow H is established by conventional structure (not shown) to extend along the longitudinal axis of the post 56 with a value resulting in gyromagnetic resonance in the ferrite material at the higher frequency of the two energies.

The energy at the resultant translated frequency is picked up by an induction coil 58 wound about the ferrite post 56. Two leads 61 and 62 of the coil 58 are respectively extended to external terminals 63 and 64 through suitable side wall apertures 66 and 67. To eliminate undesired frequency components at terminals 63 and 64 a variable tuning capacitor 69 is connected between such terminals to form a resonant circuit with the inductance of coil 58.

As previously stated, operation of the embodiment of Figure 3 is substantially the same as set forth for the device of Figure 1. Thus, with port 52 coupled to a conventional high frequency source (not shown) and port 53 coupled to a conventional lower frequency source (not shown), two waves of energy are propagated by the waveguide. Both of the waves have the same mode, such as the TE with plane polarized magnetic fields parallel to the broad walls. At the ferrite post 56, which is not critical with respect to location in the waveguide 51, the components of the magnetic fields of both modes are transverse to the longitudinal axis of the post 58 and, therefore, to the static magnetic field H Gyromagnetic precession then occurs and energy is coupled to orthogonal modes at the sum and difference frequencies. The magnetic fields of these orthogonal modes than link pickup coil 58 to induce signals and, by suitable control of tuning capacitor 69, a signal at a single frequency is developed between terminals 63 and 64. The several operating conditions set forth with respect to the embodiment of Figures 1 and 2 are equally applicable to the present embodiment for frequency translations and also for amplification.

Thus, there have been described two ferrite microwave devices which operate in substantially the same manner, but differ substantially in structure, to accomplish the objects and advantages of the invention as set forth. While thesalient features of the invention have been described in detail with respect to such devices, it will be readily apparent that many modifications may be made within the spirit and scope of the invention and it is, therefore, not desired to limit the invention to the exact details except insofar as they may be defined in the following claims.

What is claimed is:

1. A microwave device comprising structure for supporting electromagnetic energy of two different frequencies in similar modes having parallel magnetic field components, an element of gyromagnetic material mounted in said structure and extended transverse to said magnetic field components whereby such components are concentrated in said material, means for establishing a static magnetic field through said material transverse to said magnetic field components at a value producing gyromagnetic resonance at the higher frequency of energy whereby energy is coupled by said material into modes at the sum and difference frequencies orthogonal to Said similar modes, and means electromagnetically coupled to fields of said sum and difference frequencies with tuning means included for selecting a signal at one such frequency.

2. Amicrowave device comprising structure for support ng electromagnetic energy of two different frequencies in similar modes having parallel magnetic field components, a ferrite element mounted in said structure and'having an axis disposed transverse to said magnetic field components, means for establishing a static magnetic field axially through said ferrite element of a. value producing gyromagnetic resonance at the higher frequency of energy whereby energy is coupled bysaid ferrite element into modes at the sum and difference frequencies orthogonal to said similar modes, a pick-up coil having its longitudinalaxis mounted along the axis of said ferrite element within said structure, and a tuning capacitor connected in parallel with said coil for selecting a signal at one of said sum and difference frequencies.

3. A ferrite microwave device comprising structure for supporting electromagnetic energy of two different frequencies, microwave energy propagating means coupled to said structure for exciting two similar modes having parallel magnetic field components at said two different frequencies, a ferrite element mounted in said structure and having an axis disposed transverse to said magnetic field components, means for establishing a static magnetic field axially through said ferrite element of a value producing gyromagnetic resonance at the higher frequency of energy whereby energy is coupled by said ferrite element into modes at the sum and difference frequencies orthogonal to said similar modes, a pick-up coil mounted with its axis along the axis of said ferrite element within said structure, and a tuning capacitor connected in parallel with said coil to provide a circuit resonant at one of said frequencies for eliminating all but said one frequency.

4. A microwave device comprising structure for supporting electromagnetic energy of two different frequencies in similar modes having parallel magnetic field components, a hollow cylinder of gyromagnetic material having a longitudinal axis mounted transverse to said magnetic field components within said structure, means for establishing a static magnetic field axially through said material at a value producing gyromagnetic resonance at the higher frequency of energy whereby energy is coupled into modes orthogonal to said similar modes, and means electromagnetically coupled to said orthogonal modes for providing an output.

5. A microwave device comprising structure for supporting energy of two different frequencies in similar modes having parallel magnetic field components coaxial with respect to an elongated conductor within said structure, a hollow cylinder of gyromagnetic material mounted in said structure and having a longitudinal axis disposed along the axis of said conductor whereby said magnetic field components are concentrated in said material, means for establishing a static magnetic field axially through said material to produce gyromagnetic resonance at the higher frequency of energy whereby energy is coupled into modes orthogonal to said similar modes, and a pick-up coil wound on said conductor whereby said orthogonal modes link said coil to induce an output voltage.

6. A ferrite microwave device comprising a coaxial section having a center conductor and outer conductor for supporting energy of two different frequencies in similar modes having parallel magnetic field components coaxial with respect to said center conductor, a ferrite cylinder mounted in said section coaxially with respect to said center conductor whereby said magnetic field components are concentrated therein, means for establishing a static magnetic field through said ferrite cylinder parallel to the axis thereof at a value to produce gyromagnetic resonance at the higher frequency of energy whereby energy is coupled into modes orthog- .6 onal to said similar modes, a coil wound on said center'conductor whereby said orthogonal modes link said coil to induce voltages, and a tuning capacitor connected in parallel with said coil to provide a resonant circuit at one frequency of induced voltage.

7. A ferrite microwave device comprising a coaxial section having a center conductor and outer conductor for supporting energy of two different frequencies, micro wave energy propagating means coupled to said structure for exciting two similar modes having parallel magnetic field components at said two different frequencies, a ferrite cylinder mounted in said section coaxially with respect to said center section whereby said magnetic field components are concentrated therein, means for establishing a static magnetic field through said ferrite cylinder parallel to the axis thereof at a value producing gyromagnetic resonance at the higher frequency of energy whereby energy is coupled into modes orthogonal to said similar modes, a pick-up coil wound on said center conductor whereby said orthogonal modes link said coil to induce voltages, and a tuning capacitor connected in parallel with said coil to provide resonance with the inductance of said coil at the frequency of one of said induced voltages.

8. A ferrite microwave device comprising a first rectangular waveguide for propagating energy in a plane polarized mode at a selected frequency, a second rectangular waveguide for propagating energy in a plane polarized mode at a lower frequency than said selected frequency, said first and second waveguides mounted with respective broad walls in parallel relation, a section of coaxial line having a center conductor and outer conductor mounted transversely between adjacent broad walls of said waveguides with adjustable coupling probes respectively extended from the ends of said center conducter into said waveguides whereby said center section is excited in two similar modes having parallel magnetic field components at said different frequencies, a ferrite cylinder mounted in said section coaxially with respect to said center conductor whereby said magnetic field components are concentrated therein, means for establishing a static magnetic field through said ferrite cylinder parallel to the axis thereof at a value producing gyromagnetic resonance at said selected frequency whereby energy is coupled into modes orthogonal to said similar modes at sum and diflerence frequencies, a pick-up coil wound on said center conductor and having leads extended through said cylinder and outer conductor whereby said orthogonal modes link said coil to induce voltages at said sum and difference frequencies, and a tuning capacitor connected between said leads to provide resonance with the inductance of said coil at the frequency of one of said sum and difference frequencies.

9. A microwave device comprising structure for supporting electromagnetic energy in two similar plane polarized modes having parallel magnetic field components and different frequencies, a gyromagnetic element mounted within said structure and having a longitudinal axis transverse to said magnetic field components, means for establishing a static magnetic field axially through said element at a value producing gyromagnetic resonance at the higher frequency of said energies whereby energy is translated to modes orthogonal to said similar modes, and means electromagnetically coupled to said orthogonal modes for deriving an output.

10. A microwave device comprising a section of rectangular waveguide for propagating energy in two similar plane polarizing modes having parallel magnetic field components at two different frequencies, a gyrornagnetic element mounted within said waveguide with an axis transverse to the broad walls and to said magnetic field components, means for establishing a static magnetic field axially through said element at a value producing gyromagnetic resonance at the higher frequency of said energies whereby energy is translated to modes orthog- '7 onal to said similar modes, and means electromagnetically coupled to said orthogonal modes for deriving an output.

11. A ferrite microwave device comprising a section of rectangular waveguide for propagating energy in two similar modes having parallel magnetic field components parallel to the broad Walls of said waveguide at two difierent frequencies, a ferrite post mounted in said wave guide with an axis disposed transversely of the broad walls, means for establishing a static magnetic field through said post along said axis at a value producing gyromagnetic resonance at the higher frequency of energy whereby energy is translated to modes orthogonal to said similar modes, and means electromagnetically coupled to said orthogonal modes for deriving an output.

12. A ferrite microwave device comprising a section of rectangular waveguide for propagating energy in two similar plane polarized modes having parallel components of magnetic field parallel to the broad walls of said waveguide at twodifierent frequencies, a cylindrical ferrite post mounted in said waveguide with an axis disposed transversely of the broad walls, means for establishing a static magnet field through said post along the axis at a value producing gyromatic resonance at'the higher frequency of energy whereby energy is translated to modes orthogonal to said similar modes, a pick up coil wound on said post whereby said orthogonal modes link said coil to induce voltages with leads extended through apertures in said waveguide, and tuning capacitor connected between said leads to provide a circuit resonant only to one of said induced voltages.

References Cited in the file of this patent UNITED STATES PATENTS 2,802,183 Read Aug. 6, I957 FOREIGN PATENTS 777,341 Great Britain June 19,1957

Disclaimer 2,936,369.Le0n J. Loader, Los Angeles, Calif. FERRITE MICROWAVE MIXER. Patent dated May 10, 1960. Disclaimer filed June 30, 1961, by the assignee, Hughes Aircraft Company. Hereby enters this disclaimer to claims 1, 9, and 10 of said patent.

[Ojficz'al Gazette August 15, 1961.]

Disclaimer 2,936,369.-Le0n J. Ladea", Los Angeles, Calif. F ERRITE MICROWAVE MIXER. Patent dated May 10, 1960. Disclaimer filed June 30, 1961, by the assignee, Hughes Aircraft Uompany. Hereby enters this disclaimer to claims 1, 9, and 10 of said patent.

[Ofiicz'al Gazette August 15, 1961.] 

